Apparatus for stressing tension members



July 22, 1969 E. E. DABNEY ETAL APPARATUS FOR STRESSING TENSION MEMBERS 5 Sheets-Sheet 1 Filed July 13, 1967 nsmm wv ND ma nm vw v P w aafm /ms T M E A UAOH EJ 22, 1969 E. E. DABNEY ETAL APPARATUS FOR STRESSING TENSION MEMBERS Filed July 13, 1967 5 Sheets-Sheet 2 INVENTORS E. DABNEY JAMES A. FIELDS LOP/5 L. 052552 CHARLES E. NEW/NS A T TOPNEY EUGENE y 22, 1959 E. E. DABNEY ETAL 3,456,918

APPARATUS FOR STRESSING TENSION MEMBERS Filed July 15, 1967 5 Sheets-Sheet 5 INVENTORS EUGENE E. DABNEY JAMES R FIELDS LOP/5 L. GERBER CHAPLE-S E. NEW/NS B Y WIREML, t A r ram/5y 22, 1969 E. E. DABNEY ETAL 3,456,918

APPARATUS FOR STRESSING TENSION MEMBERS Filed July 13, 1967 5 Sheets-Sheet 4 EUGENE E. DABIVEY JAMES R. FIELDS LOR/S L. GERBER CHARLES E. NEW/NS Fig.9 .BY 294i A T TOR/V5 Y "4- 0 E 4/ W INVENTORS Jul 22, 1969 E. E. DABNEY ETAL v APPARATUS FOR STRESSING TENSION MEMBERS 5 Sheets-Sheet 5 Filed July 13, 1967 ws m w 9M &3 n WWW 3 w 3 E G n a mv mm 2 Mi Q@ a o I. e M a Q Q 0 7 U sa ml mmCw .f\ a W J w YR NLY TlIJ mm Q L A MN MN \Q\ INVENTORS EUGENE E. DAB/VEY JAMES P. FIELDS LOP/5' L. GERBER CHARLES E NEW/N5 dydlfim ATTORNEY United States Patent 9 M 3,456,918 APPARATUS FOR STRESSING TENSION MEMBERS Eugene E. Dabney, James R. Fields, and Loris L. Gerber,

Corpus Christi, Tex., and Charles E. Newins, Lafayette,

Califl, assignors to The Prescou Corporation, a corporation of Texas Filed July 13, 1967, Ser. No. 653,238

Int. Cl. E04c 3/12 U.S. Cl. 254-29 11 Claims ABSTRACT OF THE DISCLOSURE Apparatus for stressing the tension members in a prestressed concrete structure comprising a wheeled carriage mounted on the top surface of a concrete structure that has a pair of jaws extending down into a pocket in the concrete structure, the jaws having a pair of wings that are spaced crosswise of the jaw with an opening between them for the tension members to extend through. The tension members have ends that terminate in the pocket, which extend through openings in plates that are mounted in the pocket with heads on the tension members engaging the plates. The plates and tension members are so arranged in the pocket that the tension members are stressed by moving the plates apart. The jaws are mounted on the carriage so as to be moved up and down into and out of the pocket and also moved toward and away from each other by a single hydraulic jack that moves the one jaw relative to the carriage while the other jaw remains fixed relative to the carriage in a horizontal direction. Two types of carriage are disclosed. In one the jaws are mounted directly on a wheel supported frame and the other a second frame is mounted on the wheel supported frame and has the pair of jaws mounted thereon. The movement up and down of the jaws is controlled either by means of a pair of hydraulic cylinders or by means of a winch construction operated by a hand crank.

One of the purposes of our invention is to provide a machine for centrally stressing tension members in a prestressed concrete structure by a post-tensioning method, in which the tension members, usually in the form of high tensile strength steel wires, are kept in a group in which the individual wires are close together. This is to avoid the unnecessary amount of pull that is required where the tension members are widely separated after leaving the concrete structure by means of such a stressing apparatus. The excessive amount of pulling that is neces' sary, where the tension members are arranged in the pocket in two transversely spaced groups, with the jaws of the stressing apparatus between them, as has been proposed in the prior art, is due to the fact that the wires or other tension members are usually caused to abruptly change direction, when such an arrangement of jaws and groups of tension members, as proposed in the prior art, is utilized. The tension members are usually grouped closely together where they come out of the concrete, in order to be put in a convenient position for tensioning and anchoring. By separating this closely adjacent set of tension members into a pair of transversely spaced groups, they are changed unnecessarily in direction, which causes excessive pulling action required to stress the same.

It is another purpose of our invention to provide a mounting for the jaws so that the same can be easily moved up and down into and out of the pocket into Patented July 22, 1969 which they are passed for engagement with the plates that are provided as anchorages on the ends of the tension members, and with means for moving the jaws relative to each other in a horizontal direction, to eliminate excessive friction losses in the transmission of the force from a hydraulic jack to such jaws and thereby to the tension members. This is accomplished by providing a carriage that is mounted on wheels, on which the jaws are mounted so that the same can be readily moved with respect to each other horizontally of the carriage. In order to simplify the structure and make it possible to provide the relative movement of the jaws in a horizontal direction or toward and away from each other, by means of a single hydraulic jack, one of the jaws is mounted on a frame so as to be only movable up and down with respect thereto while the other jaw is mounted for movement on the frame toward and away from said first said mentioned jaw, by means of the hydraulic jack, the mounting comprising rollers carried by a member movable with said other jaw that are mounted in the frame for guided movement lengthwise of said frame. Preferably the rollers are provided with antifriction means for reducing the forces required for moving said movable jaw relative to the stationary jaw.

Other objects and advantages of our invention will appear as the description of the drawings proceeds. We desire to have it understood however that we do not intend to limit ourselves to the particular details shown or described except as defined in the claims.

In the drawings:

FIG. 1 is a view in side elevation of my improved stressing machine in position on a slab with the stressing jaws in elevated position and in close adjacency,

FIG. 2 is an end elevation thereof partly broken away as viewed from the line 22 in FIG. 1,

FIG. 3 is a top plan view of our stressing machine,

FIG. 4 is a fragmentary bottom plan view looking upwardly at the jaws and their mounting,

FIG. 5 is a side elevation partly broken away of a modified form of our invention,

FIG. 6 is an end elevation partly broken away as viewed from the line 6-6 of FIG. 5,

FIG. 7 is a bottom plan view, looking upwardly at the stressing jaws and their mounting, showing a pair of anchor plates engaged thereby in the position that the same have prior to stressing of the tension members,

FIG. 8 is a similar view showing the plates in the position that they will assume after the tension members have been stressed, and showing a shim mounted between them for holding the plates in stressing position,

FIG. 9 is a fragmentary view partly in section taken on line 99 FIG. 3,

.FIG. 10 is a vertical sectional view, partly broken away, of a concrete structure showing a fragmentary portion of our stressing machine mounted thereon,

FIG. 11 is a section taken on the line 1111 FIG. 10 on an enlarged scale,

FIG. 12 is a similar sectional view taken on line 1212 FIG. 10, and

FIG. 13 is a section taken on line 13-13 FIG. 10 on an enlarged scale.

Referring in detail to the drawings, a carriage is shown in FIGS. 1 to 3 inclusive, that is provided with a pair of longitudinally extending frame members 10 that connect a pair of transversely extending frame members 11 each of which have a pair of vertically extending legs 12 and 'upper transverse frame members 13 that connect said vertically extending portions 12. The frame members 11 at the rear end of the frame have depending brackets 14 mounted thereon in fixed position on which the wheels 15 provided with pneumatic tires 16 are mounted to turn about suitable fixed axes. The frame members 11 at the forward end of the frame are provided with suitable swivel means 17 from which brackets 18 extend downwardly for mounting the wheels 19 thereon to rotate about suitable axes provided on said brackets, said wheels having pneumatic tires 20 provided thereon. The wheels 19 are thus swivelly mounted with respect to the frame.

A bracket 21 extends forwardly from each of the wheel mounting brackets 18 and a bracket 22 is provided on the end of each of said brackets 21, which bracket 22 is mounted to swivel about a vertical axis on the bracket 21 and is provided with means for mounting a transverse rod 23 connecting said brackets for rotation about an axis extending longitudinally of said rod. Extending upwardly from the rod 23 is a handle 24 which is secured in fixed position on said transverse rod 23 by suitable means such as the gusset plates 25 shown in edge view in FIG. 3. The carriage is thus mounted on wheeled supporting means in such a manner that it can be moved about and guided into a position with respect to a pocket in a concrete structure so that the stressing jaws provided thereon can be successfully lowered into and moved to ward and away from each other in said pocket.

Mounted on the vehicle frame for vertical movement up and down with respect to the same, is a second frame having the longitudinal members 26 which are connected at one end thereof by means of a transverse frame member 27 and at the other end thereof by means of a block 28. Said longitudinal frame members 26 are provided with a plurality of laterally extending flanges 29, and the transverse portions 13 of the frame members 11 are provided with upstanding flanges 30 that are provided with openings 31, which may be engaged by suitable hoisting means for moving the stressing apparatus into position on a concrete structure in connection with which it is to be used.

Mounted on the transverse frame member 27 and extending endwise from the frame is a hydraulic cylinder 32 of a hydraulic jack that is provided with a piston within the same from which the piston rod 33 extends, said hydraulic cylinder being provided with suitable hydraulic fluid connections 34 and 35, which can be utilized alternately either as hydraulic inlet or outlet connections, in order to operate the piston in the cylinder either toward the left or right as may be found desirable to operate the machine. Mounted on an enlargement 36 on the extremity of the piston rod 33 is a block 37 which is the body portion of the movable stressing jaw mounting. Said block is mounted so as to be freely movable between the longitudinal frame members 26 and has a tapering downward extension 38 terminating in a pair of transversely spaced depending flanges 39. Mounted in the block 37 is a pair of transversely extending shafts 40, which are provided with rollers 41 On the ends thereof, said rollers being preferably provided with suitable antifriction hearing means mounting the same on said shafts. The rollers 41 are seated in longitudinally extending grooves 42 that are provided in the longitudinal frame members 26 and serve as guides in which the rollers 41 operate so as to obtain guided movement of the movable stressing jaw with respect to the frame upon which the same is mounted, see FIGS. 3 and 9.

Mounted between the flanges 39 is the movable stressing jaw, which is provided with a transversely extending top wall portion 43 that engages the underface of tapered portion 38 of the block 37 between the flanges 39. Said stressing jaw has a pair of depending wings 44 that are spaced transversely of said stressing jaw and which wings are provided with thickened portions 45 and 46 along the vertical margins thereof, providing a pair of outwardly directed flanges 47 and a pair of inwardly directed flanges 48 on said wings. The flanges 47 engage the vertical edges of the depending flanges 39 and the inwardly directed flanges 48 provide shoulders that extend vertically of said wings for engagement of an anchor plate therewith. The wing portions 44 are secured to the flanges 39 by any suitable securing means and the stress that is exerted on said wings, when the tension members are being stressed, is transmitted by means of the outwardly directed flanges 47 to the edge portions of the flanges 39 engaged thereby. Ample space is provided between the inwardly directed flanges 48 to provide for the passage of the wires or other tension members between the same.

The block 28 is the body portion of the mounting means for the stationary stressing jaw. Said block is provided with a tapering portion 38, corresponding to the portion 38 described in connection with the block 37, and has a pair of transversely spaced depending flanges 39 thereon, which are of the same character as the depending flanges 39 on the block 37. The stationary stressing jaw is a duplicate of the movable stressing jaw and is mounted on the block 28 in the same manner as the movable stressing jaw is mounted on the block 37. The same reference numerals are applied to the parts of the stationary stressing jaw as to the parts of the movable stressing jaw as they correspond in arrangement and function to those of the movable stressing jaw.

The stressing jaws in FIGS. 1, 2 and 4 are shown without any anchor plates engaged therewith, while in FIGS. 7, 8, 11 and 12 anchor plates are shown in engagement with said stressing jaws. The anchor plate 49 is shown as being in engagement with the shoulders 48 on the wings 44 of the movable stressing jaw and the anchor plate 50 is shown as being in engagement with the shoulders 48 on the wings 44 of the fixed stressing jaw, in FIGS. 7, 8, 11 and 12. The stressing jaws are shown in their raised position in FIGS. 1 and 2 and in their lowered position in FIGS. 7, 8, 10, 11 and 12.

The means for raising and lowering the stressing jaws between these two positions, in the form of the invention shown in FIGS. 1 to 3 inclusive, comprises suspending means for the frame upon which the jaws are mounted which is provided with means for raising and lowering said jaw supporting frame. Shaft portions 51 and 52 are mounted in suitable bearings in the vertical portions of 12 of the frame members 11 and in a reduction gearing 53. The hand crank 54 is mounted for rotation on the housing 55 of the reduction gearing, having suitable driving connections between the crank shaft 56 and the reduction gearing to drive the shaft portions 51 and 52 at a reduced rate as the crank 54 is operated in either direction, the shaft portions 51 and 52 being driven in the same direction simultaneously. Mounted on the shaft portions 51 and 52 are winding drums 57 on which the wire cables 58 are adapted to be wound. The cables 58 pass over the sheaves 59 and 60 mounted in suitable bearings on the frame members 11, said flexible members 58 extending downwardly from the sheaves 60 to suitable securing means on the block 28 and the hydraulic cylinder 32, so as to be fixed at their ends to the block 28 and the hydraulic cylinder 32. It will be obvious that rotation of the crank 54 in one direction will raise the entire assembly comprising the longitudinal frame members 26 the block 28 and the hydraulic cylinder 32 and rotation of said crank in the opposite direction will move said assembly downwardly, the crank 54 being thus utilized for moving the stressing jaws to a raised position when the apparatus is to be transported from one place to another on the concrete structure and to lower the stressing jaws from the position shown in FIGS. 1 to 3 inclusive to a position into the pocket in the concrete for engagement of the achor plates therewith.

In FIG. 7 the anchor plate 50 is shown as being engaged by a head 61 on a wire tendon 62 which extends toward the left and is secured to a dead end anchor at the opposite end thereof. The head 63 on the tendon 64,

extending toward the right in FIG. 6 and having a dead head anchorage provided on the right-hand end of said tendon, is shown in engagement with the anchor plate 49. The parts are shown in FIG. 7 in the position that they have before the stressing of the tendons has taken place. The length of the tendons is such that they will be in proper position for stressing upon movement of the anchor plates out of the position shown in FIG. 7. The tendons being of such a length that they have to be pulled slightly to engage the anchor plates 49 and 50 with the shoulders 48 on the stressing jaws. This slight pull of the tendons is suflicient to hold the anchor plates 49 and 50 in engagement with said shoulders 48, with the parts in the position shown in FIG. 7.

In FIG. 8 the tendons 62 and 64 are shown as having been stressed, the anchor plates 49 and 50 having been moved apart a greater distance than that shown in FIG. 7 so as to put the proper tension on the tendons 62 and 64. After this has been done a shim 65 is placed in position between the plates 49 and 50 to hold the same in their tendon stressing position. The stressing jaws can then be raised up out of their engaging position with the plates 49 and 50 and the stressing apparatus moved to another position. While one tension member 62 and one tension member 64 only is shown in FIGS. 7 and 8, this is only for purposes of illustration as is also true of the showing of four tension members 62 and four tension members 64 in FIGS. 10, 11 and 12. The number of tension members in each group is ordinarily considerably greater than that illustrated. Also the arrangement of tension members in the position in which the same pass through the anchor plates 49 and 50 may be varied from that shown.

Upon reference to FIGS. 10, 11 and 12 it will be noted that the concrete structure 66 has a flat top face 67 upon which the wheels of the carriage of the central stressing machine are mounted. The concrete structure is shown as being provided with a pocket 68 into which the tension members 62 and 64 extend and in which the anchor plates 49 and 50 are located. It will also be noted that the relative position of the tension members, in a group that is connected to a single anchor plate, is preferably such that the wires or other tension members 64 are in close adjacency in the body of the concrete, except at the extreme ends of said tension members. A desirable arrangement of the tension members in the main body portion of the concrete is shown in FIG. 13. However, at the anchored ends thereof the tension members separate somewhat and are arranged as shown in FIGS. 11 and 12, which is substantially the arrangement thereof where they emerge from the concrete as they enter the pocket 68. While only four wires are shown in each group several times that many may be in each tendon and connected to a single anchor plate. Each group comprising a tendon has lubricant applied to the wires thereof, and is enclosed in a sheath 69. The remote ends of the tendons have the heads on the wires engaging a dead end anchor plate 70 as shown at the left of FIG. 10.

The wrapped tendons with the anchor plates attached thereto are mounted in the form for the concrete structure 66 and have the ends thereof carrying the anchor plates 49 and 50 mounted in the form in such a position that they will be in the pocket 68 after the concrete is poured. The wires 64 pass through openings in the anchor plate 50 and through openings in the anchor plate 49 with the heads 63 thereon engaging with the left-hand face of the anchor plate 49 as viewed in the drawings. The wires 62 pass through openings in the anchor plate 49 and through openings in the anchor plate 50 with the heads 61 thereon in engagement with the right-hand face of the anchor plate 50. After the concrete has been poured and has set then the central stressing machine is put in position on the top surface 67 of the concrete structure 66 with the jaws thereon in position to be lowered into the pocket. The jaws are then lowered into the pocket 68 with the wires 62 and 64 located between the two wings of each of the jaws, and the anchor plates 49 and 50 are engaged with the shoulders 48 on the jaws. Enough of a pull has to be exerted on the wires 62 and 64, to bring about this engagement, that the anchor plates 49 and 50 will be held in engagement with the shoulders 48. Suitable valve means between the hydraulic pressure means and the hydraulic cylinder 32 is then adjusted so that the hydraulic fluid connection 35 becomes an inlet connection and the hydraulic fluid connection 34 becomes an outlet connection whereupon the piston in the hydraulic cylinder 32 is moved to the left to move the movable jaw of the stressing apparatus to the left. This is continued until the desired movement has taken place to put the tension members 62 and 64 under the desired stress. This mov ement is illustrated diagrammatically in FIG. 8, the parts being shown in the position which they will assume after the stress has been put on the wires 62 and 64. A shim 65 is then inserted between the anchor plates 49 and 50, and after the shim is in position, the fluid connections are reversed so that the fluid connection 34 becomes the inlet connection and the fluid connection 35 the outlet connection to release the jaws from the anchor plates 49 and 50, whereupon the hoisting apparatus for the movable frame carrying the stressing jaws is moved upwardly from the position shown in FIG. 10 to that shown in FIGS. 1 and 2. Then the central stressing apparatus is moved to a new location over another pocket 68. Upon disengagement of the stressing jaws from the anchor plates, the anchor plates will move to such a positionthat the stress will be equalized as between the wires 62 and 64. The pocket from which the jaws have been removed can now be filled with concrete when desired.

Referring now to FIGS. 5 and 6, a modified form of the invention is shown which provides for the mounting of the frame carrying the gripping jaws directly on a wheeled support without having a complete vehicle frame. The frame carrying the gripping jaws is mounted on a pair of end frame members 71 which are provided with guides 72, angular in cross section, and which are adapted to receive upright angular members 73, which are mounted on the longitudinal frame members 26' which correspond to the longitudinal frame members 26 provided in the form of the invention shown in FIGS. 1 to 4 inclusive. The frame members 71 are provided with depending brackets 14 which are similar to the brackets 14 previously described and which are mounted in fixed position on the rear frame member 71 of the carriage. Wheels 15 provided with pneumatic tires 16 are provided on the bracket members 14' in the same manner as previously described. The frame members 71 at the forward end of the carriage are provided with brackets 18', which are swivelly mounted thereon in a similar manner to the brackets 18 previously described and have the wheels 19 provided with the tires 20 mounted thereon. Suitable means may be provided for pulling the carriage about attached to the brackets 18 in a similar manner to that shown in FIG. 3 for the form of the invention shown in FIGS. 1 to 4 inclusive.

The frame having the side members 26 is a duplicate of the frame shown in FIGS. 1 to 4 inclusive, having the blocks 28 and 37 provided thereon and having the hydraulic cylinder 32 mounted thereon in a similar manner to that previously described. The block 28 serves as means for mounting the stationary jaw which is provided with the top wall 43 engaging the under side of the tapering end portion 38' of the block 28 and having its wing portions mounted between the flanges 39' on said block 28. The stationary and movable stressing jaws are made exactly in the same manner in this form of the invention as previously described and the same reference numerals are applied to the corresponding parts thereof in FIGS. 5 and 6, the movable stressing jaw being mounted between the flanges 39 on the lower end portion of the block 37 as in the form of the invention shown in FIGS. 1 to 4 inclusive.

The frame members 71 have upwardly extending converging legs 74 which are connected by means of a transverse member 75. On each of the transverse members 75 a bracket 76 is mounted which is provided with a pair of pivot ears 77 for pivotally mounting the end portion of a piston rod 78 thereon which is connected with a piston in a hydraulic cylinder 79 which is provided with hydraulic fluid connections 80 and 81. Cross members 82 extend between the frame members 26 at opposite ends thereof and are provided with suitable screw threaded openings for receiving the screw threaded members 83 extending from the lower ends of the hydraulic cylinders 79.

It will be obvious that the frame comprising the longitudinal member 26' the cross member 27 the block 28 and the block 37 can be raised and lowered so that it may be moved, from the position shown in FIGS. 5 and 6 downwardly into a position within a pocket in a concrete structure, by supplying hydraulic fluid to the cylinders 79 simultaneously to move the pistons therein downwardly, the hydraulic fluid connection 80 serving as a hydraulic fluid inlet connection in this case. Similarly when it is desired to raise the stressing jaws out of the pocket in the concrete the hydraulic fluid can be supplied to the connection 81 and discharged through the connection 80 to raise the pistons in the cylinders 79 to bring the stressing jaws back into the position shown in FIGS. 4 and 5 of the drawings. Suitable valve means can be provided for controlling the supply of hydraulic pressure to the two hydraulic cylinders 79 in such a manner as to simultaneously move the pistons up or down as desired. The hydraulic cylinder 32 operates in the same manner as previously described to move the movable stressing jaw back and forth with respect to the fixed stressing jaw in the manner previously described in connection with FIGS. 1 to 4 inclusive.

What we claim is:

1. The combination with a concrete structure having a top surface provided with a pocket therein, tension members terminating in said pocket, plates having openings through which said tension members extend in a predetermined area thereof, and heads on said tension members engaging said plates, of means for relatively moving said plates to stress said tension members comprising a carriage mounted on said surface, a pair of stressing jaws mounted on said carriage for movement into and out of said pocket, each of said jaws having a pair of transversely spaced relatively fixed wings defining an opening between the same, said wings engaging spaced areas of said plates and the area having said openings aligning with the opening between said wings, and means on said carriage for moving one of said jaws toward and away from said other aw.

2. The combination claimed in claim 1 in which said carriage comprises a wheel supported frame, a jaw supporting frame, said stressing jaws depending from said jaw supporting frame, and said means for mounting said jaws for movement into and out of said pocket comprising means mounting said jaw supporting frame for movement up and down relative to said wheel supported frame and means for moving said jaw supporting frame up and down relative to said wheel supported frame.

3. The combination claimed in claim 2 in which one of said stressing jaws is mounted in fixed position on said jaw supporting frame, said other stressing jaw is mounted on said jaw supporting frame for guided movement toward and away from said one jaw and fluid pressure operated means for moving said other jaw relative to said one jaw on said jaw supporting frame.

4. The combination claimed in claim 1 in which a frame is mounted on said carriage for up and down movement relative thereto, means is mounted on said carriage for moving said frame up and down, said frame comprising longitudinal frame members having longitudinally ex;

tending guides thereon, one of said jaws is fixed on said frame, the other jaw has roller means engaging said guides, and fluid pressure means mounted on said frame for moving said other jaw longitudinally of said longitudinal frame members.

5 An apparatus for stressing the tension members in a prestressed concrete structure comprising a wheeled carriage, a pair of stressing jaws mounted on said carriage for movement into and out of depending position with respect to said carriage, and means on said carriage for moving one of said jaws toward and away from said other jaw comprising a frame having a pair of longitudinal members each provided with longitudinally extending guide slots, one of said jaws being fixed to said frame at one end thereof, paired rollers on said other jaw, each pair engaging in one of said guide slots and fluid pressure means mounted on said frame for moving said other jaw longitudinally of said longitudinal frame members.

6. An apparatus for stressing the tension members in a prestressed concrete structure comprising a carriage, a pair of stressing jaws mounted on said carriage for movement into and out of depending position with respect to said carriage, each of said jaws having a pair of trans versely spaced relatively fixed wings defining an opening between the same, inwardly directed transversely spaced and transversely aligned flanges on each pair of wings, and means on said carriage for moving one of said jaws toward and away from said other jaw.

7. The apparatus claimed in claim 6 in which a frame is mounted on said carriage for up and down movement relative thereto, means is mounted on said carriage for moving said frame up and down, said frame comprising longitudinal frame members having longitudinally extending guides thereon, one of said jaws is fixed on said frame, the other jaw has roller means engaging said guides, and fluid pressure means mounted on said frame for moving said other jaw longitudinally of said longitudinal frame members.

8. The apparatus claimed in claim 6 in which said stressing jaws are mounted on a frame, and means is provided for mounting said frame on said carriage for movement up and down on said carriage comprising a pair of upwardly projecting frames on said carriage, hydraulic cylinders each having one relatively movable element thereof connected with one of said upwardly projecting frames and the other relatively movable element thereof connected with said first mentioned frame, and means for supplying hydraulic fluid to opposite ends of said cylinders.

9. The apparatus claimed in claim 6 in which said carriage comprises a wheel supported frame and a jaw supporting frame, and said means for mounting said jaws for movement into and out of depending position with respect to said carriage comprises means for mounting said jaw supporting frame for movement up and down relative to said wheel supported frame and means for moving said jaw supporting frame up and down relative to said wheel supported frame.

10. The apparatus claimed in claim 9 in which one of said stressing jaws is mounted in fixed position on said jaw supporting frame, said other stressing jaw is mounted on said jaw supporting frame for guided movement toward and away from said one jaw and fluid pressure operated means for moving said other jaw relative to said one jaw on said jaw supporting frame.

11. The apparatus claimed in claim 9 in which said wheel supported frame is provided with means for mounting a pair of flexible members thereon to suspend said jaw supporting frame from said wheel supported frame, said means including a pulley over which each of said flexible members extends, means mounting said pulleys on said wheel supported frame over the opposite ends of said jaw supporting frame, a winding drum for each of said 9 10 flexible members on said Wheel supported frame and 2,696,040 12/1954 Crom et a1. common means for simultaneously rotating said drums 3,285,569 11/1966 La Marr et a1. 254-29 in the same direction. 3,290,005 12/1966 Beemsterboer et a1. 254-18 References Cited MILTON S. MEHR, Primary Examiner 5 UNITED STATES PATENTS Us Cl. XR' 3,263,384 8/1966 Middendorf 52223 X 29-452; 52-223 3,371,909 3/1968 Stinton 2s4 29 

